couple bonehead super basic physics questions about radio and batteries.

Discussion in 'OnBoard Electronics & Controls' started by Squidly-Diddly, Nov 28, 2017.

  1. Squidly-Diddly
    Joined: Sep 2007
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    Squidly-Diddly Senior Member

    1) how do radios work? I get that they send out elector-magnetic waves, and higher freq = shorter waves, etc. How does the freq of the signal created by the crystal change? Does the crystal's freq change with diff levels of input power? I've got a basic HAM lic (tech class) but none of the study materials seemed to address the super basic stuff.

    What is happening at the basic physics atomic level in these crystals?Rectifier - Wikipedia Something similar to how a Septic Tank system will expel water periodically in set large amounts once triggered by fullness?

    2) what does a "battery checker" read to tell the health/lifespan of a battery?AA/AAA/C/D/9V Universal Button Cell Battery Volt Tester Checker US Seller | eBay

    What part of I=V/R is it testing on standard disposable DC batts? Aren't these batts designed to provide pretty close to rated volts and amps over their lifespan? How does the checker tell how much "gas is in the tank"?

    Unfortunately, I just tossed all my old questionable used battery collection. Any links to what is going on in a typical DC battery as it ages, or how much juice it still could produce at lower levels after its past its prime? I used to run AAA in a "head light"2000LM LED 3 Mode Headlamp AAA Headlight Adjustable Camping Torch Lamp Light | eBay and when they would no longer work I'd run them the rest of the way down in a small radio.

    Portable Battery Load Tester | 6V 12V Diagnostic Charging System 100amp Car Boat | eBay

    I hear these can tell if a battery is "good"(not junk) whether or not it has a full charge. What is happening chemistry/physics wise as a standard lead/acid car battery ages? IIRC even near dead batts will read about 12V.
  2. Barry
    Joined: Mar 2002
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    Barry Senior Member

    The website, Battery University has a lot of info about batteries, the processes, charging etc

    Regarding the 100 amp tester. While they might be somewhat accurate, you should test the battery at a current load of 1/2 the CCA of the battery and the 100 amp unit does not put this draw on the battery.
    You hook up the battery, turn the switch and crank the dial until it reaches the 1/2 the CCA, for 15 seconds ( might be a little less and the instructions that come with the load tester will tell you) Most testers will beep at the correct time
    interval. At the end of the 15 second draw, look at the scale, read the voltage, compare it to the chart to see if the battery voltage falls within the acceptable range. Many scales will just show "good" or "weak"

    You could spend about $80 US for a large enough tester.
  3. Barry
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    Barry Senior Member

  4. Ike
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    Ike Senior Member

    Without getting too technical I will try to explain. (for those of you with electronics background, please bear with me. This is very simplistic and a lot of stuff is left out)
    Radios create a signal called a carrier wave. This wave is at a constant frequency and amplitude. The frequency you set on your radio is the frequency of the carrier wave. For instance, an AM radio set at 100 Kilohertz (or kilocycles) is broadcasting or receiving a carrier wave at that frequency. The carrier wave is modified either in amplitude (AM radio) or in frequency, by an audio wave (something you can hear). At the broadcasting end the carrier is modified in amplitude or frequency and then transmitted. At the receiving end the antenna detects the carrier, and then the carrier is stripped away leaving only the audio frequencies which is then amplified and you hear it in the speakers or headphones.

    Crystals: If you impose a current on a certain type of crystal it will resonate at a frequency depending on the amount of current. However most modern radios do not use crystals, they use electronic components to create the carrier wave. But you can still buy crystal radio kits that you assemble. They are a great teaching tool. Most require no batteries. The pressure of a needle on the crystal excites the electrons in the crystal.

    Battery University is a very good resource. For more also look at

  5. CDK
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    CDK retired engineer

    The radio transmitter employs one or more quartz crystals to generate stable carrier frequencies. In FM transmitters the resonance frequency is tuned (shifted) with a small diode (voltage dependent capacitor). The change is very small: for a 100 Mhz oscillator 0.005 % is enough for speech modulation.
    Modern radios use frequency synthesis instead of quartz crystals because that is smaller and cheaper.

    The battery tester measures the internal resistance of a battery by comparing the output voltage with and without a load.
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